The proper functioning of tissues and organs requires polarized cells. Cells acquire polarized morphologies (i.e., differences in subcellular composition from one side of the cell to the other) through various mechanisms, including the planar cell polarity (PCP) pathway, which is the subject of this proposal. A number of molecular components of the PCP pathway have been characterized, including the upstream transmembrane Fz receptor and the downstream factors, disheveled, prickle, strabismus, flamingo, and others. The PCP pathway is responsible for generating polarized cell morphologies and behaviors, and for coordinating polarity on a tissue-wide scale. Much about the PCP pathway remains poorly understood, including the mechanisms that link PCP machinery to polarization of structural and functional components of the cell, and the mechanism by which the polarity of tissues and organs is determined at a global level. This application proposes to use the notochord of the tunicate Ciona as a model to study the PCP pathway. Tunicates are the closest extant relatives of vertebrates, but have much smaller genomes, and simpler, though similar, morphology. This simplicity is seen in the Ciona notochord which consists of only forty cells. In the Ciona notochord, PCP-dependant mechanisms are responsible, first, for the directed intercalation of cells in the medio/lateral axis to form a column. At the completion of intercalation, the PCP pathway signals a second polarization of the notochord cells, this time in the anterior/posterior axis. Experiments proposed in the first specific aim will more fully characterize Ciona notochord polarity by examining the temporal and spatial changes in core PCP protein localization, and will address the transition from medio/lateral to anterior/posterior polarity and how these two polarities are linked. The second specific aim will investigate mechanisms by which global polarity is established and the role of cell-to-cell signaling in propagation and maintenance of polarity. Finally, the third specific aim will attempt to uncover the molecular identity(ies) of the global polarizing signals acting both in the medio/lateral and anterior/posterior axes. PUBLIC HEALTH RELEVANCE: Defects in cell polarity are associated with many human disease conditions, such as polycystic kidney disease. The proposal will investigate the fundamental cellular mechanism that underlies the formation of cell polarities.